1. Field of the Invention
The present invention relates to balloon catheters useful in medical dilatation procedures.
2. Description of the Prior Art
Angioplasty has gained wide acceptance in recent years as a efficient and effective method for treating types of vascular diseases. In particular, angioplasty is widely used for opening stenoses in the coronary arteries, and is also used for treatment of stenoses in other parts of the vascular system.
The most widely used form of angioplasty makes use of a dilatation catheter which has an inflatable balloon at its distal end. Using fluoroscopy, the physician guides the catheter through the vascular system until the balloon is positioned across the stenosis. The balloon is then inflated by supplying fluid under pressure through an inflation lumen to the balloon. The inflation of the balloon causes stretching of the artery and pressing of the lesion into the artery wall to reestablish acceptable blood flow through the artery.
In order to treat very tight stenosis with small openings, there has been a continuing effort to reduce the profile of the catheter so that the catheter not only can reach but also can cross such a very tight stenosis. An important factor in the profile of the dilatation catheter is the wall thickness of the balloon material.
Balloons for dilatation balloon catheters have been made from a wide variety of polymeric materials. Typically the balloon wall thicknesses have been on the order of 0.002 to 0.003 inches with most materials. There have been continuing efforts, however, to develop thin wall balloon materials which have much thinner walls than the standard wall thicknesses (and thus are capable of lower profile) while still having the necessary distensibility and burst pressure rating. One example of a thin wall balloon is described in the Levy U.S. Pat. No. 4,490,421. In the Levy patent, molded balloons made of a polyethylene terephthalate (PET) homopolyester are described. PET-balloons having wall thicknesses on the order of 0.0002 inches have been developed.
Despite the advantage of very thin walls, PET balloons have been found to have a number of significant disadvantages. First, PET balloons formed by blow molding can exhibit pinholes which can emit a high velocity jet of inflation fluid during inflation. This jet can cause artery dissection. Second, PET exhibits low tear resistance. Third, PET balloons will not distend more than about 5%, so that higher inflation pressures will not allow the physician to fully open a stenosis if the balloon proves to be slightly smaller than what is needed. Fourth, PET balloons are very susceptible to damage, and can not be touched. Fifth, PET will not take a crease ( which is advantageous for folding the balloon).
There is a continuing need for improved balloon catheters and, in particular, for alternative thin wall balloon materials and fabrication methods.